Bis-.beta.-hydroxy alkyl ethers of halogenated bisphenols are known and are used as hydroxy components for the production of flame resistant synthetic resins. These bis-ethers are generally solid, crystalline or vitreous (i.e. glass-like) resins. The esters produced from these ethers and dicarboxylic acids are also known and have already been used in the production of flameproof plastics. Canadian Pat. No. 663,542 relates, for example, to the production of an ester by esterifying bis-.beta.-hydroxy ethyl dibromobisphenol and 1,2-propylene glycol with a mixture of phthalic acid anhydride and maleic acid anhydride. This ester contains 25.2% of bromine and is a glass-like resin at room temperature. However, to produce polyurethane and polyisocyanurate plastics, it is advantageous for the starting components to be in the form of low-viscosity liquids to enable the foaming mixture to be poured.
Polyethers containing free hydroxyl groups such as, for example, polyethylene glycol or polypropylene glycol, have long been used as low-viscosity components for the production of polyurethane and polyisocyanurate plastics. The polyethers of bisphenols containing hydroxyl groups are also known for this purpose. However, it is apparent from U.S. application Ser. No. 373,230, filed June 25, 1973, now abandoned, that polyethers of halogenated bisphenols cannot be produced under normal manufacturing conditions. The treatment of highly halogenated bisphenols, such as, tetrabromobisphenol, with alkylene oxides in the formation of bis-ethers of the kind referred to above, even in cases where an excess of alkylene oxide is used.
It would be an obvious solution to dissolve these bis-ethers in low-viscosity polyalkylene glycols in order to incorporate them as halogen carriers into the foaming mixture for producing substantially non-inflammable plastics. Unfortunately, the solubility of these bis-ethers in hydroxyl compounds of this kind is very poor. The ether quickly crystallizes out from solutions in which it is present in the high concentrations required, or alternatively the solution solidifies into a solid crystalline mass which can no longer be poured. According to U.S. Application No. 373,230, it is possible to obtain low-viscosity, pourable polyether derivatives of halogenated bisphenols. To achieve this, the polyethers of halogen-free bisphenols containing hydroxyl groups are initially prepared in known manner and are subsequently halogenated by treatment with elemental halogen, such as bromine. The polyethers thus obtained have a pourable consistency and the foams produced from them, especially polyisocyanurate foams, show outstanding flameproof properties. Unfortunately, they have the disadvantage that they tend to turn brittle at their surface and they exhibit poor bond strength with surface layers. In addition, the process described in the aforementioned U.S. application is complicated by the fact that polyetherification and halogenation are two completely different reactions each of which has to be carried out in specially designed apparatus and, hence, in two separate production units. The considerable outlay on apparatus (the use of corrosion-proof apparatus, for example, of special steels) involved in halogenation necessitates obtaining as high a degree of halogenation as possible in order to make the fullest possible use of the reaction. Accordingly, it is more rational, in order to produce a halogen-containing, substantially non-inflammable plastic or intermediate product, to start with a highly halogenated starting material than it is to subsequently halogenate the particular plastics material used or the intermediate product to a correspondingly lower degree of halogenation.